1. Field of the Invention
The present invention relates generally to flat panel displays (FPDs), and more specifically to field emission displays (FEDs). Even more specifically, the present invention relates to supporting a faceplate of an FED under vacuum.
2. Discussion of the Related Art
A field emission display (FED) is a low power, flat cathode ray tube type display that uses a matrix-addressed cold cathode to produce light from a screen coated with phosphor materials. FEDs provide a relatively thin display device that can achieve CRT-like performance; however, FEDs are inherently difficult to manufacture.
Typically, an FED includes a cathode plate containing an electron emitting surface that when driven, emits electrons toward a thin glass faceplate or anode plate coated with patterned phosphor. However, in order to allow free flow of electrons from the cathode plate to the phosphors and to prevent chemical contamination (e.g., oxidation of the electron emitters), the cathode plate and the anode plate are sealed within a vacuum.
It is important in FEDs that the particle emitting surface of the cathode plate and the opposed display face or anode plate be maintained insulated from one another at a relatively small, but uniform distance from one another throughout the full extent of the display face. Additionally, there is a relatively high voltage differential, e.g., generally above 200 volts, between the cathode emitting surface and the display face. It is important that electrical breakdown between the emitting surface and the display face be prevented. However, the space between the two plates has to be small to assure the desired thinness and that the high resolution is achieved. This spacing also has to be uniform for uniform resolution, uniform brightness, to avoid display distortion, etc. Nonuniformity in spacing can occur in FEDs since there typically is a high differential pressure on the opposed or exterior side of the display face, e.g., whereas the exposed side of the display face is at atmospheric pressure, a high vacuum of less than 10−6 torr, generally is applied between the cathode structure and the interior side of the display face.
In order to maintain the separation between the cathode plate and the anode plate (display face) across the dimensions of the FED in the pressure of the vacuum, structurally rigid spacers are positioned between the cathode plate and the anode plate. The design and manufacture of these spacers is one of the most difficult aspects in making FEDs. Without the spacers, the display face would deform due to the pressure of the vacuum, or worse yet collapse upon the cathode plate resulting in a voltage short between the cathode plate and the display face. Additionally, if the arrangement of the spacers is not properly registered, electrons emitted from the cathode array will be intercepted before striking a phosphor coated display face, materially affecting the brightness.
Disadvantageously, the spacers of the FED are visible to a viewer looking closely at the display. As such, there have been many attempts to design spacers in order to minimize their appearance. For example, spacers have been designed as walls or ribs (e.g., having an aspect ratio 50×1000 μm) extending between the cathode and anode plates or designed as other structures, such as balls, crosses and stars. However, this has proved an insurmountable task, e.g., as far as the inventors are aware, the spacers of all currently manufactured FEDs are visible upon inspection.
Traditionally, FEDs have been used as small, thin display devices, for example, display devices having 2–10 inch display screens and a total thickness of less than 10 mm, e.g., the thickness of the display face or the anode plate is typically about 1 mm. The largest known FEDs are approximately 10–12 inch displays. Many have attempted to develop FEDs as an alternative the liquid crystal displays (LCDs) for thin display devices, such as laptop or notebook computer displays; however, the larger the display device, the more difficult it is to maintain uniform separation between the cathode plate and the anode plate across the full dimensions of the display in the vacuum since the area of the cathode and anode plates has increased.